Coupling Between Functionality and Trafficking to the Axon Initial Segment in KCNQ2/3 K ⁺ Channels

KCNQ2/3 are the predominant voltage-gated K ⁺ channels localized at the axon initial segment (AIS), the critical site for the initiation of action potentials and the plasticity of excitability. Both the functionality and spatial distribution of KCNQ2/3 provide the basis for the regulation of neuronal excitability and the pathogenesis of various neurological disorders, including epilepsy. However, less is known about how functionality is coupled with trafficking regulation in KCNQ2/3. Here, we study the AIS localization of KCNQ2/3 by performing both multiple- and single-molecule imaging analyses. We found that low-activity mutations in the KCNQ3 subunit affect all of the 3D dynamics composed of lateral diffusion and exo/endocytosis processes through disruption of interaction with ankyrin-G, consequently suppressing the AIS targeting of KCNQ2/3. Thus, the functionality of KCNQ2/3 is coupled with its trafficking regulation, enhancing our understanding of the mechanisms underlying physiological and pathophysiological changes in neuronal excitability.